An overcurrent display device of this type detects an overcurrent selectively and a display member of the device is actuated mechanically. The electric power necessary for actuating the device and controlling circuit associated therewith is taken from a distribution cable through a current transformer. The electric power obtained in this manner is restricted generally in magnitude and it is rather difficult to provide a reliable display of the overcurrent condition with this electric power.
On the other hand, when a current transformer, i.e. a principal member to sense an overcurrent, is replaced by another transformer of different output property, trouble arises in adjusting the sensing and controlling circuit to operate satisfactorily. In some cases, misoperations of the overcurrent display device cannot be prevented.
Furthermore, the overcurrent display device must be suspended directly from a cable for a long time without maintenance. Consequently the magnetic properties of the current transformer must be stable over the long time, and the whole device must be compact, duarable and lightweight. The device needs waterproof and rust prevention.